On board present aircraft the batteries used are mainly cadmium nickel their ? [ Candidate qualification ]

Question 26-1 : 3 4 5 6 3 4 6 7 2 3 4 5 6 1 2 5 6 7

The terminal voltage remains substantially constant at about 1 2 volts throughout most of the discharge due to its low internal resistance it is also capable of supply high current during its discharge cycle and low current during recharging without violent fluctuations of terminal voltage .nicad batteries have a low thermal capacity the heat generated in certain conditions is faster than it can dissipate so causing rapid increase in temperature .this has the effect of lowering the effective internal resistance thus allowing an ever increasing charging current which unless checked leads to the total destruction of the battery

A static inverter is powered by ?

Question 26-2 : Direct current on input alternating current output alternating current on input direct current on output alternating current on input alternating current on output direct current on input direct current on output

exemple 130 Direct current on input, alternating current output. — .an inverter is a unit used to convert dc into ac .dc to ac inverter .ac to dc rectifier Direct current on input, alternating current output.

The voltage regulator of a dc generator is connected in ?

Question 26-3 : Series with the shunt field coil series with the armature parallel with the shunt field coil parallel with the armature

exemple 134 Series with the shunt field coil. — On a dc generator voltage regulation is achieved by changing the voltage in the voltage coil which changes the carbon pile pressure which changes the current in the shunt field the voltage regulator is connected in series with the shunt field coil Series with the shunt field coil.

During start of an engine fitted with a brushless ac generator with no ?

Question 26-4 : A set of permanent magnets the main field winding the stabiliser winding jointly with the voltage regulator the auxiliary winding

exemple 138 A set of permanent magnets. — A set of permanent magnets.

The type of windings commonly used in dc starter motors are ?

Question 26-5 : Series wound shunt wound series shunt wound compound wound

exemple 142 Series wound. — Dc motors are classified as to the ways in wich their field excitation circuits are arranged series wound shunt wound compound wound the series wound motors have their field and armature windings in series with each other so the same current flows through both adding them together . these motors have a high starting torque especially as in the initial stages there is little back emf so all the current is used in them they are commonly used as starter motors Series wound.

The power output of a generator is controlled by ?

Question 26-6 : Varying the field strength varying the speed of the engine the reverse current relay circuit breaker varying the length of wire in the armature windings

exemple 146 Varying the field strength. — The only practical method of controlling the output voltage of a generator is to control the strength of the magnetic field by controlling the current flow in a coil wound around the magnetic pole pieces field coil or field winding control of the current flow is achieved by a voltage regulator .the voltage regulator senses the output voltage of the generator or alternator and adjusts the field current to maintain the correct output voltage irrespective of generator speed or electrical load Varying the field strength.

A relay is ?

Question 26-7 : A magnetically operated switch another name for a solenoid valve a unit that is used to convert electrical energy to heat energy a device that is used to increase electrical power

exemple 150 A magnetically operated switch. — A magnetically operated switch.

The voltage of a fully charged lead acid battery cell is ?

Question 26-8 : 2 2 volts 1 4 volts 1 8 volts 1 2 volts

The capacity of a battery is given in ?

Question 26-9 : Ampere hours amperes/volts watts ohms

exemple 158 Ampere hours. — Ampere hours.

A relay is ?

Question 26-10 : An electromagnetically operated switch an electrical security switch a switch specially designed for ac circuits an electrical energy conversion unit

exemple 162 An electromagnetically operated switch. — An electromagnetically operated switch.

The most widely used electrical frequency in aircraft is ?

Question 26-11 : 400 hz 200 hz 50 hz 60 hz

If the electrical load of an ac generator providing a constant output voltage ?

Question 26-12 : Increase the intensity of the excitation current change the direction of the excitation current maintain the intensity of the excitation current constant decrease the intensity of the excitation current

exemple 170 Increase the intensity of the excitation current. — The output is regulated by varying the current to the field windings the voltage regulator senses the alternator output and adjusts the field current when a voltage rises above a set value typically 115 5 v the current is cut off around 2000 times a second the voltage regulator is there to stop the battery being overcharged or the system being overloaded Increase the intensity of the excitation current.

The so called 'hot buses' or 'direct buses' are ?

Question 26-13 : Directly connected to the battery kept in operating conditions by an electrical resistance in the case of energy failure automatically connected to the battery if generators have failed providing an alternative current

exemple 174 Directly connected to the battery. — Directly connected to the battery.

The reason for using inverters in an electrical system is ?

Question 26-14 : To change dc into ac to change the dc voltage to change ac into dc to avoid a short circuit

exemple 178 To change dc into ac. — To change dc into ac.

The function of a constant speed drive csd is to ensure ?

Question 26-15 : That the generator produces a constant frequency that the starter motor maintains a constant rpm irrespective of engine acceleration/deceleration that the csd output remains at a constant rpm irrespective of generator rpm an equal ac voltage output from all generators

A bus bar is ?

Question 26-16 : A distribution point for electrical power a device which may only be used in dc circuits the stator of a moving coil instrument a device permitting operation of two or more switches together

exemple 186 A distribution point for electrical power. — A distribution point for electrical power.

A csd of an ac generator may be disconnected in flight the primary reason s for ?

Question 26-17 : Low oil pressure and/or high oil temperature of the generator drive slight variation about the normal operating frequency excessive variation of voltage and kvar illumination of the csd disconnect warning light

A csd unit which has been disconnected in flight ?

Question 26-18 : May be reset on the ground only after engine shut down automatically resets at engine shut down automatically resets in flight providing engine rpm is below a given value may be reset in flight using the reset mechanism

exemple 194 May be reset on the ground only, after engine shut-down. — May be reset on the ground only, after engine shut-down.

Because of the input/output relationship of an or gate it is often referred to ?

Question 26-19 : 'any' or 'all' gate 'all or nothing' gate 'state indicator' gate 'inhibited' or 'negated' gate

exemple 198 'any' or 'all' gate. — 'any' or 'all' gate.

Connecting two 12 volt 40 ampere hour capacity batteries in series will result ?

Question 26-20 : 24 volts 40 ampere hours 12 volts 80 ampere hours 12 volts 40 ampere hours 24 volts 80 ampere hours

exemple 202 24 volts, 40 ampere-hours. — 24 volts, 40 ampere-hours.

When a conductor cuts the flux of a magnetic field ?

Question 26-21 : An electromotive force emf is induced in the conductor there will be no effect on the conductor current will flow in accordance with flemings left hand rule the field will collapse

exemple 206 An electromotive force (emf) is induced in the conductor. — .when a current is passed through the wire wrapped around a conductor its magnetic field penetrates the conductor and causes the domains to turn aligning parallel to the magnetic field so their tiny magnetic fields add to the wire's field creating a large magnetic field that extends into the space around the magnet . the larger the current passed through the wire coil the more the domains align and the stronger the magnetic field is An electromotive force (emf) is induced in the conductor.

In order that dc generators will achieve equal load sharing when operating in ?

Question 26-22 : Their voltages are almost equal equal loads are connected to each generator busbar before paralleling adequate voltage differences exist the synchronising bus bar is disconnected from the busbar system

exemple 210 Their voltages are almost equal. — When two dc generators are operating in parallel control of load sharing is achieved by an equalising circuit which in conjunction with the voltage regulators varies the field excitation current of the generators Their voltages are almost equal.

The purpose of a voltage regulator is to control the output voltage of the ?

Question 26-23 : Generator at varying loads and speeds batteries at varying loads generators at varying speeds and the batteries at varying loads tru

exemple 214 Generator at varying loads and speeds. — For dc generators the voltage regulation is achieved by changing the voltage in the voltage coil which changes the carbon pile pressure which changes the current in the shunt field this then is the reactive load wasted power that adjusts the energising current the same principle applies in ac generators alternators but they use solid state circuitry Generator at varying loads and speeds.

A current limiter fuse in a dc generation system is used to ?

Question 26-24 : Allow a short term overload before rupturing limit the current in the field circuit allow no overload before rupturing limit the current in the armature

exemple 218 Allow a short term overload before rupturing. — A fuse is a deliberately weak part of a circuit that is designed to fail if a problems occurs current limiters are like fuses but with a much higher melting point so that a higher overload current can be carried they allow a short term overload they will limit the current to a predetermined value and are used for heavy duty circuits Allow a short term overload before rupturing.

A 3 phase ac generator has 3 separate stator windings spaced at ?

Question 26-25 : 120° 60° 45° 90°

A csd unit is normally provided with means of monitoring during flight the ?

Question 26-26 : Oil temperature and pressure oil temperature and synchronous speed output voltage and oil pressure oil temperature and quantity only

exemple 226 Oil temperature and pressure. — Oil temperature and pressure.

The phase relationship between two unparalleled ac generators ?

Question 26-27 : Is unimportant must be synchronous must be in opposition must be 90° out of synchronisation

exemple 230 Is unimportant. — Is unimportant.

Assuming a csd fault is indicated the csd should be disconnected ?

Question 26-28 : Provided the engine is running at flight idle engine rpm on the ground only when the ac generator voltage is outside limits

exemple 234 Provided the engine is running. — The function of a constant speed drive csd is to ensure that the ac generator produces a constant frequency in case of csd fault you must disconnect it if the engine is running if not since the ac generator is not rotating you don't need to disconnect it .a csd unit which has been disconnected may be reset on the ground only after engine shut down Provided the engine is running.

Ac generators operated in parallel must have the same ?

Question 26-29 : Voltage and phase voltage and amperage amperage and kvar frequency and amperage

exemple 238 Voltage and phase. — Two ac generators operated in parallel must be not only at the same speed voltage but also the same phase to be paralleled Voltage and phase.

The measured output power components of a constant frequency ac system are ?

Question 26-30 : Kva and kvar volts and amperes volts and kilowatts amperes and kilowatts

'frequency wild' in relation to a ac generation system means the generator ?

Question 26-31 : Output frequency varies with engine speed output frequency is too high output frequency is too low voltage regulator is out of adjustment

exemple 246 Output frequency varies with engine speed. — Output frequency varies with engine speed.

When the ac voltage across a capacitor is kept constant and the frequency is ?

Question 26-32 : Increase remain the same be zero decrease

exemple 250 Increase. — Capacitive reactance .when frequency tends to zero current magnitude is almost equal to zero .at contrary when fequency is high this is the magnitude of the voltage which tends to zero . 876.we are talking about capacitive reactance xc expresses in ohm Increase.

In an aeroplane fitted with a constant frequency ac power supply dc power is ?

Question 26-33 : Transformer rectifier unit tru static inverter 3 phase current transformer unit rotary converter

exemple 254 Transformer rectifier unit (tru). — Transformer rectifier unit (tru).

On an aeroplane using ac as primary power supply the batteries are charged in ?

Question 26-34 : A transformer rectifier unit a static inverter a dc transformer and rectifier the ac bus via current limiters

exemple 258 A transformer rectifier unit. — A transformer rectifier unit.

Immediately after starting engine s with no other electrical services switched ?

Question 26-35 : Would be normal and is only cause for concern if the high charge rate persists indicates a generator failure thus requiring the engine to be shut down immediately indicates a faulty reverse current relay indicates a battery failure since there should be no immediate charge

exemple 262 Would be normal and is only cause for concern if the high charge rate persists. — If the engine was started electrically using the battery there would have been a significant drain on the battery .the ammeter shows a charge after start up to replenish the energy just drained from the battery Would be normal and is only cause for concern if the high charge rate persists.

Circuit breakers protecting circuits may be ?

Question 26-36 : Used in ac and dc circuits used only in ac circuits used only in dc circuits reset at any time

exemple 266 Used in ac and dc circuits. — Used in ac and dc circuits.

The function of a csd in an ac generating system is to ?

Question 26-37 : Drive the generator at a constant speed vary the engine rpm within limits to compensate for various ac loads vary generator rpm in order to compensate for various ac loads directly maintain a constant proportion between the rpm of engine and generator

exemple 270 Drive the generator at a constant speed. — Drive the generator at a constant speed.

Because of the input/output relationship of an and gate it is often referred to ?

Question 26-38 : 'all or nothing' gate 'any or all' gate 'state indicator' gate 'inhibited' or 'negated' gate

exemple 274 'all or nothing' gate. — 'all or nothing' gate.

The function of a not logic gate within a circuit is to ?

Question 26-39 : Invert the input signal such that the output is always of the opposite state ensure the input signal is ac only ensure the input signal is dc only ensure the output signal is of the same state as the input signal

exemple 278 Invert the input signal such that the output is always of the opposite state. — Invert the input signal such that the output is always of the opposite state.

When two dc generators are operating in parallel control of load sharing is ?

Question 26-40 : An equalising circuit which in conjunction with the voltage regulators varies the field excitation current of the generators an equalising circuit which in turn controls the speed of the generators carrying out systematic load shedding procedures the synchronous bus bar

exemple 282 An equalising circuit which, in conjunction with the voltage regulators, varies the field excitation current of the generators. — An equalising circuit which, in conjunction with the voltage regulators, varies the field excitation current of the generators.

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